GB1566335A - Moulds - Google Patents

Description

PATENT SPECIFICATION

( 11) 1 566 335 ( 21) Application No 13706/77 ( 31) Convention Application No 676227 ( 33) United States of America (US) ( 44) ( 22) Filed 31 Mar 1977 ( 32) Filed 12 Apr 1976 Complete Specification Published 30 Apr 1980 ( 51) INT CL 3 ( 52) B 29 C 13/00 Index at Acceptance B 5 A 1 R 165 1 R 168 1 R 413 7 A T 12 P ( 72) Inventor: WILLIAM S BLAZEK ( 54) IMPROVEMENTS IN OR RELATING TO MOLDS ( 71) We, TRW INC, a corporation organzed under the laws of the State of Ohio, United States of America, of 23555 Euclid Avenue, Cleveland, Ohio 44117, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the follow-

ing statement:-

The present invention relates generally to improvements in or relating to a method of making at least a portion of a ceramic mold having a cavity for accurately forming a cast product and more specifically to a method of accurately making ceramic mold surfaces by reinforcing relatively flexible pattern material to prevent flexing of the pattern material as it is dipped in a slurry of ceramic mold material.

Relatively large turbine engine components, such as diffuser cases, nozzle rings, vane assemblies, bearing supports and fan frames have been previously fabricated from a multitude of small castings, sheet panels, and forgings An improved method of making a mold assembly for use in casting these products is disclosed in our copending Patent Application No 1592/77 (Serial No.

1565893) and comprises a method wherein wax patterns are dipped in a slurry of ceramic mold material to eventually form a plurality of mold sections The mold sections are interconnected to define a mold cavity in which a cast part is formed During the assembly of a jet engine fan frame mold in the manner disclosed in the above application, it has been determined that dimensional errors resulted in the fan frame due to deflection of the relatively flexible wax pattern material during dipping of the patterns.

The present invention (the scope of which is defined in the appended claims) includes a method of making at least a portion of a ceramic mold having a cavity for accurately forming a cast product, said method comprising the steps of forming a pattern assembly which at least partially defines a surface of mold cavity in which the cast product is to be formed which assembly has a pair of spaced apart and relatively thick main sections which main sections at last partially correspond to a pair of spaced apart and relatively wide sections of the mold cavity in which the cast product is to be formed, and which main sections are interconnected by a relatively thin section which at least partially corresponds to a relatively narrow section of the mold cavity in which the cast product is to be formed, said step of forming the pattern assembly including the steps of providing relatively flexible and destructible pattern material and a rigid reinforcing means comprising either a first reinforcing member at a first one of the main sections and a second reinforcing member at a second one of the main sections or a single reinforcing member at and extending between said main sections, repetitively dipping the pattern assembly in liquid ceramic mold material to form a covering of ceramic mold material overlying at least a portion of the pattern assembly, retarding deflection of the relatively flexible pattern material with the rigid reinforcing means during said dipping steps, at least partially drying the mold material, destroying the pattern material to expose a ceramic mold material surface which defines at least a portion of the surface of the mold cavity in which the cast product is formed, and removing the reinforcing means from the ceramic mold material.

The invention also includes a method of making a ceramic mold for accurately forming a cast product, said method comprising the steps of forming a plurality of pattern assemblies including the steps of providing a plurality of bodies of relatively flexible and ( 19) 1 566 335 destructible pattern material each of which has a surface area with a configuration similar to the configuration of a portion of the surface area of the cast product and providing a plurality of relatively rigid members which reinforce at least a portion of an associated one of the bodies of pattern material, said step of providing a plurality of bodies of pattern material includes the step of providing a plurality of bodies of pattern material each of which has a pair of spaced apart and relatively thick main sections which at least partially correspond to a pair of spaced apart and relatively wide sections of the mold cavity in which the cast product is formed, said main sections of pattern material being interconnected by a relatively thin arcuately curved section which corresponds to a relatively narrow section of the mold cavity in which the cast product is formed, said step of providing a plurality of reinforcing members including the step of providing a reinforcing member in association with each of said main sections of pattern material, repetitively dip coating each of the pattern assemblies in liquid ceramic mold material to form a covering of ceramic mold material overlying at least a portion of each of said plurality of pattern assemblies, retarding deflection of the bodies of relatively flexible pattern material with the rigid reinforcing members during said dipping steps, at least partially drying the mold material, providing a plurality of separate mold sections each of which has a surface area with a configuration similar to the configuration of a portion of the surface area of the cast product by destroying the bodies of pattern material and removing the reinforcing members, and interconnecting the mold sections to at least partially define a mold cavity.

In the preferred embodiments of the invention, described hereinafter, the dimensional accuracy with which cast parts are formed in ceramic molds is substantially increased by reinforcing the portion of the pattern which corresponds to the mold cavity in which a cast part is formed This reinforcing retards deflection of the pattern during dipping in a liquid ceramic mold material By reinforcing the portion of the pattern which is utilized to cast the inner or hub section of a jet engine fan frame, the amount of diametral error in a hub having a diameter of approximately 24 inches was reducted from approximately 0 360 inches to approximately 0 027 inches.

Heretofore, a cluster of wax patterns for forming cast products has been strengthened by providing relatively rigid reinforcing members in the gating and sprue cup associated with the pattern clusters The manner in which this is done is disclosed in U S Patent Specification No 2,994,931.

Although reinforcing the gating associated with a cluster of patterns may, to a limited extent, tend to retard deflection of the patterns, it is believed that this arrangement is less than optimum to form a cast product 70 In the preferred embodiments the dimensional accuracy with which a cast product is formed is enhanced by providing reinforcing in the portion of the pattern corresponding to the cast product It should be understood 75 that as used herein in both the specification and claims, the term "cast product" means the final product of a casting operation and does not include any metal which may remain in the gating which is associated with 80 the product during the casting operation In this regard, it should be noted that during certain casting operations the gating may not even be completely filled with metal but will merely serve as a partially filled reser 85 voir to supply the molten metal to the cast product The dimensional accuracy with which the gating is formed is of minimal consequence while the dimensional accuracy with which the cast product is formed is 90 of utmost importance.

In order that the invention may be well understood two preferred embodiments thereof will now be described in more detail, by way of example only, with refer 95 ence to the accompanying drawings, in which:Figure 1 is a schematic illustration of a pattern assembly; Figure 2 is a schematic illustration depict 100 ing how reinforcing members in the pattern material of the assembly of Figure 2 are engaged to support the assembly for dipping in liquid ceramic mold material; Figure 3 is a schematic sectional view 105 illustrating the relationship between a pair of mold sections or pieces formed by dipping the pattern assembly of Figure 1 in ceramic mold material after destroying the body of relatively flexible and destructable 110 pattern material and prior to removing of reinforcing members; Figure 4 is a schematic sectional view, generally similar to Figure 3, illustrating the mold sections in an interconnected condi 115 tion partially defining a cavity in which a cast product is to be formed; Figure 5 is a sectional plan view of a mold assembly formed by a plurality of mold sections similar to the mold sections shown 120 in Figure 4 and defining a generally ringshaped mold cavity in which a circular cast product is to be formed; Figure 6 is an illustration, on a reduced scale, depicting a pattern assembly in which 125 alternative reinforcing means are employed the pattern assembly being illustrated after dipping in liquid ceramic mold material; and Figure 7 is an enlarged sectional view, taken generally along the lines 7-7 of Figure 130 1 566 335 6.

A pattern assembly 10 includes a body 12 of relatively flexible and destructable pattern material, such as wax or plastic Relatively rigid reinforcing means comprising metal reinforcing members 16 and 18 is provided in the body 12 of pattern material to retard deflection of the pattern material.

The pattern assembly 10 is advantageously held in a relatively rigid frame 22 (Figure 2) as it is dipped in liquid ceramic mold material.

After the pattern assembly 10 has been dipped in liquid ceramic mold material, minor end surface 26 and 28 (see Figures 1 and 2) of the pattern assembly are wiped to at least partially remove the wet coating of ceramic mold material overlying these surfaces In addition, arcuate flange surfaces 32 and 34 (see Figure 1) are also wiped to remove the ceramic mold material.

Although the surfaces 26, 28, 32 and 34 could be wiped after each of a series of dipping steps, it is contemplated that the wiping operation may be omitted after the first dipping step to form a relatively thin layer of ceramic mold material over the surfaces 26, 28, 32 and 34 The subsequent wet coatings of ceramic mold material are wiped away in the same manner as described in our copending Patent application No 1592/77 (Serial No 1565893).

After the pattern assembly 10 has been repetitively dipped in liquid ceramic mold material and portions of a wet coating of ceramic material wiped away, the pattern assembly is fired at a relatively high temperature to thoroughly dry the layers of ceramic mold material and to destroy the body 12 of the pattern material This results in the formation of a pair of rigid ceramic mold sections 38 and 40 (see Figure 3) After any relatively thin layer of ceramic mold material that was left on surfaces 26, 28, 32 and 34 has been broken away After the body 12 of pattern material has been destroyed, the metal reinforcing members 16 and 18 will remain in the space between the mold sections 38 and 40 Once the reinforcing members 16 and 18 have been removed intact without damaging the mold sections 38 and 40, the mold sections are interconnected in the manner shown in Figure 4 to at least partially define a mold cavity 44 in which a cast product is formed Thus, the mold section 38 has a surface 46 which partially defines a surface of the mold cavity 44 The mold section 40 has a surface 48 which defines another surface portion of the mold cavity 44 The surfaces 46 and 48 were accurately formed by the surfaces of the body 12 of pattern material.

A plurality of arcuately curved mold sections 38 and 40 are made from reinforced pattern assemblies having the same construction as the pattern assembly 10 The plurality of mold sections 38 and 40 are assembled in a pair of concentric circular arrays in the manner illustrated schematically in Figure 5 to provide the mold cavity 44 with a circular ring-shaped configuration.

Although it is contemplated that the mold sections 38 and 40 can be interconnected in many different ways to form the circular mold cavity 44, the mold sections 38 and 40 are advantageously interconnected in the manner disclosed in our aforementioned copending application No 1592/77 (Serial No 1565893 to form a mold cavity in which a turbine engine component is cast It should be noted that when the mold sections 38 and 40 are interconnected in circular arrays in the manner illustrated in Figure 5, the surfaces 46 on the mold sections 38 define a radially inner surface of the circular mold cavity 44 while the surfaces 48 on the outer mold sections 40 define the outer surface of the mold cavity.

The relatively rigid metal reinforcing members 16 and 18 retard deflection of the relatively flexible wax or polymeric body 12 of pattern material as the mold assembly is dipped Of course, retarding flexing or deflection of the body 12 of pattern material during dipping increases the accuracy with which the mold sections 38 and 40 and the product forming surfaces 46 and 48 thereon are formed Although the extent to which the use of the rigid reinforcing members 16 and 18 will improve the dimensional accuracy with which the mold sections, in one illustrative instance the diametral error in the formation of a hub wall of a turbine engine fan frame having a diameter of approximately 24 inches was reduced from a diametral error of about 0 360 inches to a diametral error of about 0 027 inches.

The body 12 of wax pattern material (see Figure 1) includes a pair of arcuately curving generally parallel elongated main or rim sections 52 and 54 which are interconnected by a relatively thin section which is an arcuately curving web or wall section 58.

The rim sections 52 and 54 are relatively thick and correspond to relatively wide annular sections 62 and 64 (Figure 4) of the mold cavity 44 On the other hand, the web section 58 (Figure 1) is relatively thin and corresponds to a relatively narrow cylindrical section 68 (Figure 4) of the mold cavity 44 The wiping surfaces 32 and 34 are formed on a pair of arcuately curving flanges 72 and 74 (Figure 1) which extend outwardly from the rim sections 52 and 54.

It should be noted that when the mold sections 38 and 40 are interconnected in the manner illustrated in Figure 4, the mold sections are moved together from their initial spacial relationship (illustrated in Figure 3) through a distance equal to the 1 566 335 radial thickness of the flanges 72 and 74 so that the ceramic material of the mold section 40 which previously overlay the sides of the flanges 72 and 74 is in abutting engagement with the mold section 38.

Due to the configuration of the pattern assembly 10, the rigid reinforcing members 16 and 18 have an elongated arcuately curving configuration corresponding to the arcuately curving configuration of the rim portions 52 and 54 of the body 12 pattern material (see Figures 1 and 2) The reinforcing members 16 and 18 are located in the body 12 of pattern material by positioning them in a suitable die into which molten wax is injected However, it is contemplated that the body 12 of wax pattern material could be formed with a suitable recess into which a reinforcing member would be inserted after the wax pattern material had been removed from the die It should be noted that the metal reinforcing members 16 and 18 reduce the amount of wax in the relatively thick main or rim sections 52 and 54 of the body 12 of pattern material to thereby reduce the amount of shrinkage which occurs when the molten wax solidifies.

Once the pattern assembly 10 has been formed in this manner, both ends of each of the longitudinally extending reinforcing members 16 and 18 are engaged by the rigid metal frame 22 to support the pattern assembly 10 for dipping Thus, the frame 22 (see Figure 2) includes a pair of rigid upper side members 78 and 80 which are connected with opposite ends of the longitudinally extending metal reinforcing member 16.

Rigid lower side members 84 and 86 of the frame 22 are connected with opposite ends of the longitudinally extending metal reinforcing member 18 The side members 78, 70, 84 and 86 of the frame 22 are interconnected by the rigid reinforcing members 16 and 18 to form a rigid structure which prevents deflection of the relatively flexible pattern material 12 during dipping It is contemplated that with certain pattern assemblies it may be desirable to engage only one end of each reinforcing member rather than both ends as described herein.

The pattern assembly 10 is dipped in a body of liquid ceramic mold material by grasping the handle 90 and lowering the pattern assembly slowly downwardly along a path extending transversely to the longitudinally extending central axis of the reinforcing members 16 and 18 and parallel to the arcuately curving major side surfaces of the body of pattern material 12 However, with certain pattern assemblies it may be desirable to move the pattern assemblies along paths extending generally parallel to longitudinal axes of reinforcing members as the pattern assemblies are dipped.

After the pattern assembly 10 has been dipped in and removed from the liquid ceramic mold material, the flange surfaces 32 and 34 (Figure 1) and end surfaces 26 and 28 (Figures 1 and 2) are wiped to remove the wet coating of ceramic mold material over 70 lying this portion of the pattern assembly.

The wet ceramic coating is then dried and the pattern assembly 10 is again dipped to form another layer The dipping, wiping and drying of the pattern assembly 10 is repe 75 ated until a covering of ceramic mold material having a desired thickness has been built up on the pattern assembly The pattern assembly 10 is then heated to a temperature sufficient to melt the wax 80 pattern material 12 to expose the mold surfaces 46 and 48 in the manner illustrated in Figure 3 The resulting mold sections 38 and 40 can then be moved apart and the rigid reinforcing members 16 and 18 re 85 moved while maintaining the accurately formed mold surfaces 46 and 48 intact.

Although it is preferred to utilize reusable metal reinforcing members 16 and 18, it is contemplated that the rigid reinforcing 90 members could be formed of a suitable heat destructable material which would be melted at a slightly higher temperature than the pattern material It is also contemplated that the pattern material could be destroyed 95 by methods other than heating, for example microwaves could be utilized if desired.

After a plurality of pattern assemblies of the same construction as the pattern assembly 10 have been dipped, the relatively 100 flexible pattern material destroyed, and the relatively rigid reinforcing members removed, the resulting mold sections 38 and are interconnected in two concentric circular arrays as illustrated in Figure 5 105 Suitable gating, such as illustrated in our aforementioned copending application No.

1592/77 (Serial No 1565893), is then connected with the resulting circular mold cavity 44 to conduct molten metal to the 110 mold cavity during a casting operation.

After the casting operation has been performed, the mold sections 38 and 40 are removed The metal in the gating is then cut away and the resulting cast product which 115 was formed in the mold cavity 44 is ready for use or additional processing steps.

In the embodiment illustrated in Figures 1-5 the pattern assemblies 10 have a configuration such that the reinforcing mem 120 bers 16 and 18 are longitudinally extending rods having arcuately curving central axes.

However, it is contemplated that other types of reinforcing means could be utilized.

For example, in the pattern assembly illus 125 trated in Figures 6 and 7 a flat metal plate is utilized to reinforce a pair of bodies of flexible pattern material which are disposed on opposite sides of the plate.

A pattern assembly 100 is illustrated in 130 1 566 335 Figures 6 and 7 after the pattern assembly has been repetitively dipped in a slurry of ceramic mold material to form multi-layered coverings or mold sections 104 and 106 overlying bodies 108 and 110 of flexible and destructable pattern material, i e wax The bodies of pattern material 108 and 110 are connected to a single reinforcing member which is a flat metal by being at and extending between relatively thick main sections of the pattern assembly reinforces the relatively flexible bodies 108 and 110 of pattern material Thus, the body 108 of pattern material has flat side surfaces 118 and 120 which are held against a major side surface 122 of the reinforcing member 114.

Similarly, flat side surfaces 124 and 126 of the body 110 of pattern material are held against a flat major side surface 130 of the reinforcing member 114.

Each time the pattern assembly 100 is dipped, minor side surfaces similar to the surfaces 134 and 136, of the reinforcing member 114 are wiped to remove the wet coating of ceramic mold material which is also removed from edge portions of the bodies 108 and 110 of flexible pattern material in the manner illustrated in Figure 7.

When a covering of ceramic mold material of a desired thickness has been built up over outer surfaces of the pattern bodies 108 and 110 by repetitively dipping the pattern assembly 100, the pattern assembly is fired and the pattern bodies 108 and 110 are melted to release the mold sections 104 and 106 from the reinforcing member 114 The mold sections 104 and 106 are advantageously utilized as end caps for a segmented mold assembly in the manner disclosed in our aforementioned copending application No 1592/77 (Serial No.

1565893) However, it should be understood that a reinforcing member similar to the reinforcing member 114 could be utilized to support flexible pattern bodies having many different configurations.

In view of the foregoing, it is apparent that an improved method of making a ceramic mold (Figure 5) having a cavity 44 in which a cast product is accurately formed includes reinforcing relatively flexible wax pattern material 12 having a configuration which corresponds to the configuration of surfaces 46 and 48 of the mold cavity The flexible pattern material 12 is supported with relatively rigid reinforcing members 16 and 18 to prevent the pattern material from deflecting during dipping of the pattern assembly 10 in liquid ceramic mold material.

Between dipping steps, portions of a wet ceramic coating are wiped away in areas between portions of the wet coating which will eventually form the mold sections 38 and 40 After the ceramic mold material on the body 12 of the pattern material has been dried, the pattern material and in some cases the reinforcing members are destroyed by heating or other methods The resulting mold sections 38 and 40 are then separated and the rigid reinforcing members 16 and 18 unless already destroyed are removed intact from between the mold sections The separate mold sections 38 and 40 are interconnected to form a cavity 44 in which a cast product is accurately formed In one specific case, a plurality of mold sections 38 and 40 were interconnected to form a circular mold cavity for a turbine engine component, i e a jet engine fan frame.

Although the use of a pair of reinforcing members 16 and 18 in association with a single body 12 of wax pattern material and the use of a single reinforcing member 114 with a pair of bodies 108 and 110 of wax pattern material have been described herein, it is contemplated that other combinations of reinforcing members and bodies of pattern material could be utilized if desired.

In fact, a relatively thin coating of wax pattern material over a metal plate can be utilized as a pattern assembly to accurately form mold surfaces It should be understood that although the ceramic mold sections 38 and 40 have been utilized to define a circular mold cavity, reinforced pattern assemblies as described could be utilized to form molds having cavities with many different types of configurations.

Claims (1)

1. WHAT WE CLAIM IS:-

   1 A method of making at least a portion of a ceramic mold having a cavity for accurately forming a cast product, said method comprising the steps of forming a pattern assembly which at least partially defines a surface of the mold cavity in which the cast product is to be formed which assembly has a pair of spaced apart and relatively thick main sections which main sections at least partially correspond to a pair of spaced apart and relatively wide sections of the mold cavity in which the cast product is to be formed, and which main sections are interconnected by a relatively thin section which at least partially corresponds to a relatively narrow section of the mold cavity in which the cast product is to be formed, said step of forming the pattern assembly including the steps of providing relatively flexible and destructible pattern material and a rigid reinforcing means comprising either a first reinforcing member at a first one of the main sections and a second reinforcing member at a second one of the main sections or a single reinforcing member at and extending between said main sections, repetitively dipping the pattern assembly in liquid ceramic mold material to form a covering of ceramic mold material overlying at least a portion of the pattern 6 1 566 335 6 assembly, retarding deflection of the relatively flexible pattern material with the rigid reinforcing means during said dipping steps, at least partially drying the mold material, destroying the pattern material to expose a ceramic mold material surface which defines at least a portion of the surface of the mold cavity in which the cast product is formed, and removing the reinforcing means from the ceramic mold material.

   2 A method as claimed in claim 1, wherein said rigid reinforcing means comprises said first and second reinforcing members which members have longitudinally extending central axes, said dipping steps including the step of moving the pattern assembly into and out of the liquid ceramic mold material along a path extending transversely to the central axes of said first and second reinforcing members.

   3 A method as claimed in claim 1 or 2, further comprising the step of at least partially supporting the pattern assembly during said dipping steps by engaging an end portion of the or at least one reinforcing member.

   4 A method as claimed in claim 1 or 2, further comprising the step of at least partially supporting the pattern assembly during said dipping steps by engaging opposite end portions of the or at least one reinforcing member.

   A method as claimed in any one of the preceding claims, further comprising the step of removing at least a portion of a wet coating of ceramic mold material from an area overlying the pattern assembly immediately after performing at least some of said dipping steps.

   6 A method as claimed in claim 5, wherein said step of removing the or each reinforcing member includes separating ceramic mold material on one side of an area where a wet coating of ceramic mold material was removed from ceramic mold material on another side of the area where the wet coating of ceramic mold material was removed.

   7 A method as claimed in any one of the preceding claims, wherein said step of removing the or each reinforcing member is performed after said step of destroying the pattern material and includes the step of moving the or each reinforcing member away from the ceramic mold material while maintaining the or each reinforcing member intact.

   for accurately forming a cast product, said method comprising the steps of forming a plurality of pattern assemblies including the steps of providing a plurality of bodies of relatively flexible and destructible pattern material each of which has a surface area with a configuration similar to the configuration of a portion of the surface area of the cast product and providing a plurality of relatively rigid members which reinforce at least a portion of an associated one of the bodies of pattern material, said step of providing a plurality of bodies of pattern material includes the step of providing a plurality of bodies of pattern material each of which has a pair of spaced apart and relatively thick main sections which at least partially correspond to a pair of spaced apart and relatively wide sections of the mold cavity in which the cast product is formed, said main sections of pattern material being interconnected by a relatively thin arcuately curved section which corresponds to a relatively narrow section of the mold cavity in which the cast product is formed, said step of providing a plurality of reinforcing members including the step of providing a reinforcing member in association with each of said main sections of pattern assemblies in liquid ceramic mold material to form a covering of ceramic mold material overlying at least a portion of each of said plurality of pattern assemblies, retarding deflection of the bodies of relatively flexible pattern material with the rigid reinforcing members during said dipping steps, at least partially drying the mold material, providing a plurality of separate mold sections each of which has a surface area with a configuration similar to the configuration of a portion of the surface area of the cast product by destroying the bodies of pattern material and removing the reinforcing members, and interconnecting the mold sections to at least partially define a mold cavity.

   9 A method as claimed in claim 8, further comprising the step of supporting each of the pattern assemblies during the dipping steps by engaging the reinforcing members.

   A method as claimed in claim 8 or 9, wherein the cast product has a generally ring-shaped cross sectional configuration, said step of providing a plurality of bodies of pattern material including the step of providing a plurality of arcuately curved bodies of pattern material, said step of providing a plurality of rigid reinforcing members including the step of providing a plurality of arcuately curved reinforcing members having substantially the same curvature as the associated bodies of pattern material, said step of interconnecting the mold sections 8 A method of making a ceramic mold 1 566 335 7 1 566 335 7 including placing the mold sections in a generally ring shaped mold cavity.

   11 A method of making at least a portion of a ceramic mold substantially as herein described with reference to the accompanying drawings.

   A.A THORNTON & CO, Chartered Patent Agents, Northumberland House, 303/306 High Holborn, London, WC 1 V 7 LE.

   Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1980.

   Published by The Patent Office, 25 Southampton Buildings, London WC 2 A IAY, from which copies may be obtained.